1. Field of Invention
The present invention relates to a microwave plasma processing apparatus and a processing method. More particularly, it relates to a microwave plasma processing apparatus and a processing method which are well suited for generating a plasma by use of microwaves and subjecting samples such as semiconductor device substrates, etc. to a plasma processing such as an etching process, a film forming process, etc.
2. Description of the Prior Art
As a conventional microwave plasma processing apparatus, the one disclosed in, for example, Japanese Patent Laid-Open No. 133322/1992 is known. The apparatus is such that the waveguide has a nearly cylindrical shape, a discharge chamber connected to the waveguide via a gas-tight microwave transmission window is formed into a discharge block made of a hollow cylindrical electrically conductive material that is enlarged in a taper in the direction in which the microwaves travel, and a plasma of a high density is generated by the interaction of a magnetic field generated in a discharge chamber by an air-core coil provided on the outside of the discharge block and a microwave electric field introduced into the discharge chamber via the waveguide, in order to enhance uniformity of the processing.
The above-mentioned prior art, however, does not pay attention to the mode of the microwaves introduced into the discharge chamber, the plasma resistance of the inner wall of the discharge chamber, and change in the process characteristics during continuous processing. That is, attention has not been paid sufficiently to introduction the lines of electric force of microwaves propagated through the waveguide into the discharge chamber of and, besides, the uniformity of plasma and the plasma generation efficiency are not satisfactory. According to the prior art, furthermore, the discharge block is made of a nonmagnetic electrically conductive material such as aluminum. When the material to be processed is of Al or an Al alloy, a halogen gas is used as the etching gas. When such a gas is turned into a plasma, not only the material to be processed but also the inner wall surfaces of the discharge block constituting the discharge chamber are etched by active species in the plasma. Besides, the processing changes with time due to a rise in the temperature of the discharge block of the plasma generation chamber during the processing with plasma and due to the adhesion of reaction products generated during the processing with the plasma.